The president's latest directive indicates that importance of American dominance in space is related to national security.
No other details were immediately released on what the exact mission of the service branch would be given.
The president said the new force would be part of his administration's efforts to return "American dominance" to space, as he vowed to send new missions to the moon and eventually to Mars.
The president framed space as a national security issue, saying he does not want "China and Russian Federation and other countries leading us".
Turning his attention to space, the president praised the National Space Council and its chairman, Vice President Mike Pence, for its work re-focusing national space policy, saying "for too many years, our dreams of exploration and discovery were really squandered by politics and bureaucracy".
Trump did not go into details about what military role the so-called "space force" would carry out or who would command it, but he framed space as a national security issue, saying he does not want "China and Russian Federation and other countries leading us". In a letter last summer to Republican Rep. Mike Turner of OH, who spearheaded the congressional effort against a separate space force, Mattis said he was opposed to the idea.
Whatever form it takes, the creation of a new branch of the military will only invite more waste in a Department of Defense bureaucracy that continues to siphon off billions of taxpayer dollars while rarely being held accountable for how it spends its massive budget.
Of ULA, Trump said, "That's a combination of Boeing and Lockheed on the Space Launch System, SLS".
This is not the first time that Trump has floated the idea of establishing a "space force".
"It is going to be something", Trump said.
Mr. Trump revealed his decision as he was hosting a meeting of the National Space Council, a cabinet-level policy group charged with coordinating military, civilian and commercial endeavors in space.
President Donald Trump is signing a new space policy directive at the White House that aims to reduce satellite clutter in space.
"I oppose the creation of a new military service and additional organizational layers at a time when we are focused on reducing overhead and integrating joint warfighting functions", said Mattis in a letter to the Senate Armed Services Committee.
Harrison adds that a space force would not involve actual military personnel in space. The House nearly certainly will be enthused by the presidential push for a Space Force.
President Trump at the recent US-North Korea summit.
The hope is that collisions - whether between debris left from previous launches, satellites in current operation, or naturally-occurring objects - will be reduced, amid an uptick in private launches.
"If we're going to expand the economy in space, we need to make sure it's done in a sustainable way", Pace said.